Color temperature (expressed in degrees Kelvin, K) is a characteristic of visible light and corresponds to the temperature of an ideal black body radiator that radiates light of comparable hue to that of the light source. While many light sources approximate black body radiators (e.g., incandescent lights), many do not (e.g., fluorescent lamps). These latter types of sources are assigned what is known as a color corrected temperature (CCT). A sources' CCT is the color temperature of a black body radiator which to a human most closely matches the light of the source. Color temperatures over 5,000K are typically referred to as cool colors (bluish white), while lower color temperatures (e.g., 2,700K-3,000K) are often referred to as warm colors (yellowish white through red). This becomes significant because the color of an object is affected by the lighting conditions under which it is viewed; that is, the scene's illuminant color. Human visual systems quickly and accurately adjust to different color temperatures so that a white object appears white to us whether it's viewed in sunlight, under overcast skies or indoors under incandescent or fluorescent light.
Digital image sensors do not naturally alter what they record as a function of illuminant color as does the human eye. The process by which a digital image system compensates for differently colored light sources is known as white balance. Automatic white balance (AWB) is integral to many digital image capture systems. The purpose of all AWB systems is to neutralize or compensate for any cast created by the color(s) of the light source(s) so that all the colors (not just white) appear as seen by a human observer at the time the image was captured. In practice, white balance allows a remapping of color values to simulate variations in ambient color temperature. An incorrect white balance can cause color shifts in a captured image.